2015-12-16 03:01:59

by Andrew Pinski

Subject: Re: [PATCH 1/2] arm64: Improve error reporting on set_pte_at() checks

On Tue, Dec 9, 2015 at 17:26:56, Catalin Marinas
<[email protected]> wrote:
>
> Currently the BUG_ON() checks do not give enough information about the PTEs being set. This patch changes BUG_ON to WARN_ONCE and dumps the values of the old and new PTEs.


This change broke building the mantis driver:

In file included from ./arch/arm64/include/asm/io.h:30:0,
from drivers/media/pci/mantis/mantis_i2c.c:21:
./arch/arm64/include/asm/pgtable.h: In function ‘set_pte_at’:
./arch/arm64/include/asm/pgtable.h:281:3: error: implicit declaration
of function ‘BUILD_BUG_ON_INVALID’
[-Werror=implicit-function-declaration]
VM_WARN_ONCE(!pte_young(pte),
^

Thanks,
Andrew Pinski

>
> Signed-off-by: Catalin Marinas <[email protected]>
> Cc: Will Deacon <[email protected]>
> ---
> arch/arm64/include/asm/pgtable.h | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/include/asm/pgtable.h
> b/arch/arm64/include/asm/pgtable.h
> index 7e074f93f383..002dc61a4dff 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -276,10 +276,13 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
> * hardware updates of the pte (ptep_set_access_flags safely changes
> * valid ptes without going through an invalid entry).
> */
> - if (IS_ENABLED(CONFIG_DEBUG_VM) && IS_ENABLED(CONFIG_ARM64_HW_AFDBM) &&
> - pte_valid(*ptep)) {
> - BUG_ON(!pte_young(pte));
> - BUG_ON(pte_write(*ptep) && !pte_dirty(pte));
> + if (IS_ENABLED(CONFIG_ARM64_HW_AFDBM) && pte_valid(*ptep)) {
> + VM_WARN_ONCE(!pte_young(pte),
> + "%s: racy access flag clearing: %016llx -> %016llx",
> + __func__, pte_val(*ptep), pte_val(pte));
> + VM_WARN_ONCE(pte_write(*ptep) && !pte_dirty(pte),
> + "%s: racy dirty state clearing: %016llx -> %016llx",
> + __func__, pte_val(*ptep), pte_val(pte));
> }
>
> set_pte(ptep, pte);
>
> _______________________________________________
> linux-arm-kernel mailing list
> [email protected]
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>
>
>
>

2015-12-16 11:16:22

by James Morse

Subject: Re: [PATCH 1/2] arm64: Improve error reporting on set_pte_at() checks

Hi Andrew,

On 16/12/15 03:01, Andrew Pinski wrote:
> On Tue, Dec 9, 2015 at 17:26:56, Catalin Marinas
> <[email protected]> wrote:
>>
>> Currently the BUG_ON() checks do not give enough information about the PTEs being set. This patch changes BUG_ON to WARN_ONCE and dumps the values of the old and new PTEs.
>
>
> This change broke building the mantis driver:
>
> In file included from ./arch/arm64/include/asm/io.h:30:0,
> from drivers/media/pci/mantis/mantis_i2c.c:21:
> ./arch/arm64/include/asm/pgtable.h: In function ‘set_pte_at’:
> ./arch/arm64/include/asm/pgtable.h:281:3: error: implicit declaration
> of function ‘BUILD_BUG_ON_INVALID’
> [-Werror=implicit-function-declaration]
> VM_WARN_ONCE(!pte_young(pte),
> ^

This is due to a missing include in include/linux/mmdebug.h, which
Julien Grall saw with CONFIG_XEN & !CONFIG_DEBUG_VM. There was some
discussion at [0], and a patch at [1].

The quick-and-dirty workaround is to toggle CONFIG_DEBUG_VM. It should
be fixed in the next rc.


Thanks,

James

[0] https://lkml.org/lkml/2015/12/14/489
[1] http://www.spinics.net/lists/linux-mm/msg98868.html